Bug 1609815 - Remove Web Replay C++ implementation. r=jgilbert,jandem,gbrown

Patch by bhackett and jlaster. Also reviewed by mccr8.

Differential Revision: https://phabricator.services.mozilla.com/D60197

dom/html/HTMLMediaElement.cpp

@@ -1179,13 +1179,6 @@ HTMLMediaElement::MediaLoadListener::OnStartRequest(nsIRequest* aRequest) {
     return NS_BINDING_ABORTED;
   }
 
-  // Media element playback is not currently supported when recording or
-  // replaying. See bug 1304146.
-  if (recordreplay::IsRecordingOrReplaying()) {
-    mElement->ReportLoadError("Media elements not available when recording");
-    return NS_ERROR_NOT_AVAILABLE;
-  }
-
   // The element is only needed until we've had a chance to call
   // InitializeDecoderForChannel. So make sure mElement is cleared here.
   RefPtr<HTMLMediaElement> element;